Principles and Practice for Biopsy Diagnosis and Management of Musculoskeletal Lesions Introduction to the Diagnosis of Musculoskeletal Lesions

Fine needle aspiration and core biopsy are used at some oncology centers as the initial technique to obtain a tissue diagnosis for mass lesions occurring within the musculoskeletal system. A majority of such lesions are in actuality metastatic deposits from a primary malignancy arising elsewhere. Metastatic neoplasms usually present little difficulty in diagnosis. Primary lesions of the musculoskeletal system are a significantly greater diagnostic challenge and many authorities in histopathology of bone and soft tissue tumors have recommended against the use of small biopsy techniques for the diagnosis of these lesions. The resistance to the use of small volume specimens, especially fine needle aspiration (FNA), results from a combination of factors including the relative rarity of these lesions, the potential for radical deforming surgery and the young age of the patients in which many of these lesions occur. Musculoskeletal sarcomas account for less than 1% of all malignant neoplasms. The infrequency of these tumors results in limited experience with their morphologic appearances among surgical pathologists and cytopathologists except for those practicing at orthopedic oncology centers. Contributing to this reduction in the utilization of small biopsy procedures is the relatively high percentage of benign proliferations (pseudosarcomas) closely resembling true sarcomas. An additional issue which has slowed the implementation of FNA for the investigation of musculoskeletal neoplasms is concern that the technique may not procure sufficient sample to obtain reliable results with a variety of ancillary techniques including immunohistochemistry and molecular diagnostics. Modern techniques and increasing familiarity with the cytologic appearance of these lesions has negated many of the above concerns. Despite reservations among many surgical pathologists and cytopathologists regarding small biopsy techniques for the diagnosis of musculoskeletal lesions, familiarity with the appearance of these tumors in cytologic and small histopathologic specimens is desirable. Many primary musculoskeletal lesions are inadvertently biopsied in the work-up of suspected metastatic disease and knowledge of their appearance is necessary for appropriate post-FNA follow-up and treatment. The relatively low cost, low patient morbidity, and reduced likelihood of biopsy related complications all favor the use of small biopsy techniques including FNA. The diagnostic biopsy must separate benign from malignant tumors, establish a grade in sarcomas, and in bone neoplasms and some soft tissue neoplasms establish a specific histologic type. Diagnostic accuracy and issues concerning the choice of biopsy technique are different for lesions arising within the bone or the soft tissues. Importantly, radiographic analysis greatly facilitates the diagnosis of osseous lesions, but has relatively little input for diagnosis of soft tissue tumors.